Reversible motor configured with motion stops for aircraft windshield wiper system

ABSTRACT

Disclosed is an aircraft windshield wiper system, having: a wiper arm; a reversible motor that drives the wiper arm, the motor including: a stator; a rotor configured to rotate relative to the stator; a forward shaft segment that is driven by the rotor and being rotationally connected to the wiper arm; an aft shaft segment that is driven by the rotor, the aft shaft segment including a forward end and an aft end; a ball nut that translates along the aft shaft segment from rotation of the aft shaft segment; a forward stop at a forward end of the aft shaft segment, configured to stop forward translational motion of the ball nut along the aft shaft segment; and an aft stop at an aft end of the aft shaft segment, configured to stop aft translational motion of the ball nut along the aft shaft segment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Indian Application No.201911050812, filed Dec. 9, 2019, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND

The embodiments herein relate to windshield wiper systems for anaircraft and more specifically to a reversible motor configured withmotion stops for such windshield wiper system.

A windshield wiper system is used on an aircraft to clean a wind shieldof the aircraft, e.g., during rain. One type of windshield wiper systemutilizes a crank rocker mechanism. In such a system, continuous rotationof a motor of the windshield wiper system is converted to oscillatorymotion at a wiper shaft that is connected the crank rocker mechanism.For such a windshield wiper system, a sweep angle of the crank rockermechanism is fixed mechanically. From this, the wiper shaft isconstrained within the intended sweep angle. Another type of windshieldwiper system utilizes a reversible brushless direct-current motor(reversible motor). Through electronic controls, the reversible motorachieves oscillatory motion directly from the motor shaft.

BRIEF SUMMARY

Disclosed is a windshield wiper system for an aircraft, comprising: awiper arm; a reversible motor that drives the wiper arm, the reversiblemotor including: a stator; a rotor configured to rotate relative to thestator; a forward shaft segment, wherein the forward shaft segment isdriven by the rotor and is rotationally connected to the wiper arm; anaft shaft segment, wherein the aft shaft segment is driven by the rotor,the aft shaft segment including a forward end and an aft end; a ballnut, wherein the ball nut translates along the aft shaft segment fromrotation of the aft shaft segment; a forward stop at a forward end ofthe aft shaft segment, configured to stop forward translational motionof the ball nut along the aft shaft segment; and an aft stop at an aftend of the aft shaft segment, configured to stop aft translationalmotion of the ball nut along the aft shaft segment.

In addition to one or more of the above disclosed aspects, or as analternate, the forward shaft segment and the aft shaft segment aresegments of a motor shaft.

In addition to one or more of the above disclosed aspects, or as analternate, the motor further includes: a housing, wherein the housinghas a forward end wall and an aft end wall, wherein: the stator and therotor are disposed within the housing; the forward shaft segment extendsthrough the forward end wall of the housing; the aft shaft segmentextends through the aft end wall of the housing; and the forward stopsurface is formed by the aft end wall of the housing.

In addition to one or more of the above disclosed aspects, or as analternate, the windshield wiper system further includes: an endcap fixedto the aft end wall of the housing, the endcap including an aft end wallspaced apart from the aft end wall of the housing, wherein: the aftshaft segment is disposed within the endcap; and the aft stop surface isdefined by the aft end wall of the endcap.

In addition to one or more of the above disclosed aspects, or as analternate: the ball nut includes a flange that defines a first passage;the windshield wiper system further includes: a first guide pinextending from the aft end wall of the housing to the aft end wall ofthe endcap such that the first guide pin is parallel to the aft shaft,wherein the first guide pin extends through the first passage in theflange of the ball nut and prevents rotation of the ball nut relative tothe stator when the aft shaft segment rotates.

In addition to one or more of the above disclosed aspects, or as analternate: a second passage is defined by the flange of the ball nut;and the windshield wiper system further includes: a second guide pinextending from the aft end wall of the housing to the aft end wall ofthe endcap such that the second guide pin is parallel to the aft shaftsegment and is spaced apart from the first guide pin, wherein the secondguide pin extends through the second passage in the flange of the ballnut.

In addition to one or more of the above disclosed aspects, or as analternate, the first guide pin and the second guide pin are connected tothe aft end wall of the housing.

In addition to one or more of the above disclosed aspects, or as analternate, the reversible motor is a reversible brushless direct-currentmotor.

In addition to one or more of the above disclosed aspects, or as analternate, the reversible motor is configured to stop responsive to theball nut contacting the aft stop while the aft shaft segment rotates.

In addition to one or more of the above disclosed aspects, or as analternate, the reversible motor is configured to stop responsive tosensing an increase in current drawn by the motor when the ball nutcontacts the aft stop while the aft shaft segment rotates.

In addition to one or more of the above disclosed aspects, or as analternate, the reversible motor is configured to stop responsive to theball nut contacting the forward stop while the aft shaft segmentrotates.

In addition to one or more of the above disclosed aspects, or as analternate, the reversible motor is configured to stop responsive tosensing an increase in current drawn by the motor when the ball nutcontacts the forward stop while the aft shaft segment rotates.

In addition to one or more of the above disclosed aspects, or as analternate, the aft shaft segment is threaded, and the system furtherincludes balls within the ball nut that engage the threads on the aftshaft segment, whereby the ball nut translates forward and aft when theaft shaft segment rotates.

In addition to one or more of the above disclosed aspects, or as analternate, the windshield wiper system further includes: a reductiongear that rotationally couples the aft shaft segment to the wiper arm.

In addition to one or more of the above disclosed aspects, or as analternate, a pinion gear is defined by the forward shaft segment, andthe pinion gear is rotationally coupled to the reduction gear.

Further disclosed is an aircraft including a windshield wiper systemhaving one or more of the above disclosed aspects.

Further disclosed is a method of operating a windshield wiper system,comprising: driving a rotor of a reversible motor relative to a statorof the reversible motor; driving an aft shaft segment of a motor shaftwith the rotor; translating a ball nut from rotation of the aft shaftsegment between a forward stop and an aft stop; and stopping thereversible motor when the ball nut contacts either of the forward stopand the aft stop while the aft shaft segment rotates.

In addition to one or more of the above disclosed aspects, or as analternate, the method further includes: driving a reduction gear with aforward shaft segment of the motor shaft and driving a wiper arm withthe reduction gear.

In addition to one or more of the above disclosed aspects, or as analternate, the method further includes: preventing rotation of the ballnut relative to the stator with a guide pin extending through a passagedefined in a flange of the ball nut, from the forward stop to the aftstop.

In addition to one or more of the above disclosed aspects, or as analternate, the method further includes: stopping the reversible motorresponsive to sensing an increase in current draw by the motor when theball nut contacts either of the forward stop and the aft stop while theaft shaft segment rotates.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a perspective view of an aircraft that may include awindshield wiper system according to a disclosed embodiment;

FIG. 2 shows a detail of section A of FIG. 1, showing aspects of awindshield wiper system according to a disclosed embodiment;

FIG. 3 shows a motor of the windshield wiper system according to adisclosed embodiment;

FIG. 4 shows a cross section of the motor along section lines B-B ofFIG. 3, showing a ball nut in a forward position, disposed against anaft end of the motor housing;

FIG. 5 shows the cross section of the motor along section lines B-B ofFIG. 3, showing the ball nut in an aft position and disposed against anaft surface of an endcap connected to the motor housing; and

FIG. 6 is a flowchart showing a method of operating a windshield wipersystem according to a disclosed embodiment.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

FIG. 1 shows an aircraft 2 having a windshield 4. As shown in FIG. 2,the aircraft 2 includes a windshield wiper system 100 for cleaning thewindshield 4, e.g., during rain. The windshield wiper system 100includes a wiper arm 110 driven by a reduction gear 120 that is poweredby a motor 130. In such systems, the wiper arm 110 can traverse a sweepangle (SA) during operation. According to one non-limiting embodimentthe wiper arm 110 is configured to sweep within a sweep angle SA of,e.g., (60) sixty degrees per sweep cycle at a rate of one hundred (100)cycles per minute (CPM).

Turning to FIG. 3-5 the motor 130 includes a motor housing 160. Themotor housing 160 includes forward and aft ends 150 a, 150 b. Asillustrated, the forward and aft ends 150 a, 150 b of the motor housing160 are spaced apart along an axis 145. Within the housing 160, themotor 130 includes a stator 155 a with associated coil windings (FIGS.4-5). A rotor 155 b (FIGS. 4-5) is configured to rotate relative to thestator 155 a based on electrical power receive through one or more leads156 (FIG. 3) extending through the housing 160. The rotor 155 b drives amotor shaft 140 a (FIGS. 4-5), which may be supported on a shaft bearing155 c (FIGS. 4-5). The motor shaft 140 a defines a forward shaft segment140 b extending along the axis 145 through the forward end 150 a of thehousing 160. The motor shaft 140 also defines an aft shaft segment 140 c(FIGS. 4-5) extending along the axis 145 through the aft end 150 b ofthe housing 160.

The motor 130 of the windshield wiper system 100 may be a reversiblebrushless direct-current motor. Through electronic control of the motor130, the motor 130 achieves oscillatory motion with the forward shaftsegment 140 b of the motor shaft 140 a. As illustrated, the forwardshaft segment 140 b drives the reduction gear 120 (FIGS. 2-3). Inaddition, the forward shaft segment 140 b includes a pinion gear profile(FIG. 3) for meshing with the reduction gear 120.

The windshield wiper system 100 includes a ball nut 210. The ball nut210 translates along the aft shaft segment 140 c from rotation of theaft shaft segment 140 c. This configuration forms a ball screw typelinear actuator. A ball screw is a mechanical linear actuator thattranslates rotational motion, i.e., the aft shaft segment 140 c, tolinear motion of the ball nut 210 with little friction. A ball screw isable to apply or withstand high thrust loads with minimum internalfriction and is machinable to close tolerances. The ball screw istherefore is generally suitable for use in situations in which requirehigh precision. The aft shaft segment 140 c is formed with a helicalraceway for engaging ball bearings 200 in the ball nut 210, which actsas a precision screw. Thus, as the aft shaft segment 140 c rotates withthe motor shaft 140 a, the rotation of the aft shaft segment 140 c isconverted to linear motion of the ball nut 210 along the axis 145.

As more clearly shown in FIGS. 4-5, a forward stop 165 a is formed bythe aft end 150 b of the housing 160. The forward stop 165 a isconfigured to stop forward translational motion of the ball nut 210along the aft shaft segment 140 c. An aft stop 165 b is located at anaft end 190 of the aft shaft segment 165 b. The aft stop 165 b isconfigured to stop aft translational motion of the ball nut 210 alongthe aft shaft segment 140 c. With this configuration, the aft shaftsegment 140 c, the ball nut 210, and the forward and aft stops 165 a,165 b together form a motion limiter located at the aft end 150 b of themotor housing 160. This configuration prevents over rotation of themotor shaft 140 a. This prevents over sweep of the wiper arm 110 (FIG.2). As a result, damage to the wiper arm 110 and aircraft 2 around thewindshield 4 (FIG. 2) is potentially avoided. As disclosed herein, whenover rotation of the motor shaft 140 a in either direction isencountered, the motor 130 is stopped. The windshield wiper system 100may thereafter be serviced as needed to restore a desired operationalstate.

Rotational motion of the ball nut 210, e.g., relative to the stator 155a is prevented with one or more guide pins 220. The guide pins 220extend from the aft end 150 b of the motor housing 160, parallel withand along-side the aft shaft segment 140 c. The ball nut 210 includes aflange 210 a, which is cylindrical and defines one or more passages 210b through which the respective one or more guide pins 220 extend. Theone or more guide pins 220 may have a same length as the aft shaftsegment 140 c to prevent run-off of the flange 210 a as the ball nut 210moves along the aft shaft segment 140 c. In the illustrated embodiment apair of the guide pins 220 are utilized, though this is not intended onlimiting the scope of the disclosed embodiments.

The aft shaft segment 140 c with the ball nut 210 and the guide pins 220are encased against the aft end 150 b of the motor housing 160 by anendcap 230. The endcap 230 is cylindrical having a sidewall 240 with aninner diameter that is larger than the flange 210 a of the ball nut 210.An aft wall 250 of the endcap 230 is located near or against an aft end190 of the aft shaft segment 140 c. The aft wall 250 of the endcap 230forms the aft stop 165 b.

The opposing radial directions in which the motor 130 rotates per wipersweep cycle are illustrated in FIGS. 4-5. The opposing radial directionsinclude a first rotational direction R1 (as illustrated in FIG. 4) and asecond rotational direction R2 (as illustrated in FIG. 5). The directionof translation D of the ball nut 210 will reverse when rotation of theaft shaft segment 140 c reverses, e.g., at each wiper sweep cycle. Theball nut 210 translates toward the aft end 150 b of the motor housingwhen the motor 130 rotates the aft shaft segment 140 c in the directionR1 during one wiper sweep cycle. The ball nut 210 translates toward theaft wall 250 of the endcap 230 when the motor 130 rotates the aft shaftsegment 140 c in the direction R2 during another wiper sweep cycle.

Further, the ball nut 210 translates, during each wiper sweep cycle, bytravel distance DT along the aft shaft segment 140 c. The traveldistance DT is a function of on a thread pitch of the aft shaft segment140 c. During movement of the ball nut 210, the aft end 150 b of themotor housing 160 and the aft wall 250 of the endcap 230, as indicatedabove, may respectively form the forward stop and the aft stop (e.g.motion stops). This configuration may prevent over travel of the ballnut 210 against the aft shaft segment 140 c during each wiper sweepcycle. Preventing the ball nut 210 from traveling beyond the traveldistance DT during each wiper sweep cycle may prevent over rotation ofthe wiper arm 110.

The following non-limiting example demonstrates a process in determiningthe travel distance DT to restrict the linear travel of the ball nut210. The process requires determining the number of complete rotationsof the aft shaft segment 140 c per wiper sweep cycle. This is a functionof the gear reduction ratio and the sweep angle SA. The process thenrequires determining the travel distance DT as a function of the numberof complete rotations of the aft shaft segment 140 c per wiper sweepcycle (calculated) and the thread pitch for the aft shaft segment 140 c.

In one non-limiting embodiment the windshield wiper system 100 isconfigured as follows: a sweep speed of the wiper arm 110 (FIG. 2) isone hundred (100) cycles per minute (CPM); a total sweep angle SA of thewiper arm 110 is sixty (60) degrees (FIG. 2); the reduction gear 120 isconfigured to provide a reduction gear ratio of fifty to one (50:1); andthe aft shaft segment 140 c is threaded, e.g., with a helical groove, atten (10) threads per inch (TPI).

The number of complete rotations of the aft shaft segment 140 c perwiper sweep cycle is calculated by a first formula of:

(gear reduction x sweep angle)±(360 degrees per rotation).

The gear reduction of fifty to one (50:1) and the sweep angle SA of thewiper arm 110 is sixty (60) degrees. Thus the first formula provides(50×60/360)=eight and a third (8.33) rotations per wiper sweep cycle.

The travel distance DT of the ball nut 210 per wiper sweep cycle iscalculated by a second formula of:

(number of completed rotations of the aft shaft segment 140 c per wipersweep cycle (calculated above))±(the thread pitch of the aft shaftsegment 140 c).

The thread pitch on the aft shaft segment 140 c is ten (10) TPI. Thusthe second formula provides (8.33/10)=(0.833) inches of travel for theball nut 210 per wiper sweep cycle. Therefore, a travel distance DT ofthe ball nut 210 can be (0.850) inches per wiper sweep cycle, accountingfor clearance.

To provide the travel distance DT for the ball nut 210, a height HC ofthe endcap 230, and length L of the aft shaft segment 140 c that extendsbeyond the aft end 150 b of the motor housing 160, are properly sized.The height HC of the endcap 230 may differ from the length L of the aftshaft segment 140 c by the thickness of the aft wall 250 of the endcap230, which may be considered nominal so these two measurements may besubstantially the same. Thus, the height HC of the endcap 230 may be atotal distance between the aft end 150 b of the motor housing 160 andthe aft wall 250 of the endcap 230. Thus, the height HC would be thetravel distance DT (calculated above), combined with a height HB (FIG.5) of the ball nut 210, which may be measured.

For design of the motor 130, it is noted that the speed in revolutionsper minute (RPM) of the aft shaft segment 140 c per wiper sweep cycle isa function of the gear reduction ratio and the sweep speed. That is, thegear reduction ratio is fifty to one (50:1) and the sweep speed of thewiper arm 110 is one hundred (100) CPM. With this, the aft shaft segment140 c will have a speed of:

gear reduction x sweep speed of wiper arm 110.

This results in (50×100), or five thousand (5000) RPM.

With the above configuration, as indicated, the ball nut 210 will beprevented from traveling more than the travel distance DT. The motor 130will be unable to produce over rotation in either direction R1 or R2 andinstead will experience an over current draw. An over current triplogic, which may be programmed into the motor 130, may execute uponsensing an over current draw from the motor 130, shutting down the motor130.

Turning to FIG. 6 a flowchart shows a method of operating the system100. As shown in block 510 the method includes driving a rotor 155 b ofa reversible motor 130 relative to a stator 155 a of the reversiblemotor 130. As shown in block 515 the method includes driving a reductiongear 120 with a forward shaft segment 140 b of the motor shaft 140 awith the rotor 155 b and driving a wiper arm 110 with the reduction gear120. As shown in block 520 the method includes driving an aft shaftsegment 140 c of a motor shaft 140 a with the rotor 155 b. As shown inblock 530 the method includes translating a ball nut 210 from rotationof the aft shaft segment 140 c between a forward stop 165 a and an aftstop 165 b. As shown in block 535 the method includes preventingrotation of the ball nut 210 relative to the stator 155 a with a guidepin 220 extending through a flange 210 a of the ball nut 210, from theforward stop 165 a to the aft stop 165 b. As shown in block 540 themethod includes stopping the reversible motor responsive to sensing anincrease in current draw by the motor when the ball nut contacts eitherof the forward stop and the aft stop while the aft shaft segmentrotates.

In sum the disclosed embodiments provide for stopping/halting rotationof a motor shaft using ball screw mechanism. The disclosed embodimentsutilize an over current-trip of the motor, where the over current-tripis activated at a locked rotor condition that occurs from stoppage ofthe ball nut. The system is formed and assembled utilizing commonmanufacturing techniques. The system is relatively easily configurable,depending largely on a sweep angle of the wiper blade arm. One benefitof the disclosed embodiments includes protecting aircraft, wipercomponents and related hardware from damage that could result from oversweep. A stopping torque required to engage the over current-trip of themotor with the disclosed embodiments is significantly decreased comparedwith motion limiters located away from the motor. The reduced wear onthe motor results in a more reliable system.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof

Those of skill in the art will appreciate that various exampleembodiments are shown and described herein, each having certain featuresin the particular embodiments, but the present disclosure is not thuslimited. Rather, the present disclosure can be modified to incorporateany number of variations, alterations, substitutions, combinations,sub-combinations, or equivalent arrangements not heretofore described,but which are commensurate with the scope of the present disclosure.Additionally, while various embodiments of the present disclosure havebeen described, it is to be understood that aspects of the presentdisclosure may include only some of the described embodiments.Accordingly, the present disclosure is not to be seen as limited by theforegoing description, but is only limited by the scope of the appendedclaims.

What is claimed is:
 1. A windshield wiper system for an aircraft, comprising: a wiper arm; a reversible motor that drives the wiper arm, the reversible motor including: a stator; a rotor configured to rotate relative to the stator; a forward shaft segment, wherein the forward shaft segment is driven by the rotor and is rotationally connected to the wiper arm; an aft shaft segment, wherein the aft shaft segment is driven by the rotor, the aft shaft segment including a forward end and an aft end; a ball nut, wherein the ball nut translates along the aft shaft segment from rotation of the aft shaft segment; a forward stop at a forward end of the aft shaft segment, configured to stop forward translational motion of the ball nut along the aft shaft segment; and an aft stop at an aft end of the aft shaft segment, configured to stop aft translational motion of the ball nut along the aft shaft segment.
 2. The windshield wiper system of claim 1, wherein the forward shaft segment and the aft shaft segment are segments of a motor shaft.
 3. The windshield wiper system of claim 1, wherein the motor further includes: a housing, wherein the housing has a forward end wall and an aft end wall, wherein: the stator and the rotor are disposed within the housing; the forward shaft segment extends through the forward end wall of the housing; the aft shaft segment extends through the aft end wall of the housing; and the forward stop surface is formed by the aft end wall of the housing.
 4. The windshield wiper system of claim 3, further comprising: an endcap fixed to the aft end wall of the housing, the endcap including an aft end wall spaced apart from the aft end wall of the housing, wherein: the aft shaft segment is disposed within the endcap; and the aft stop surface is defined by the aft end wall of the endcap.
 5. The windshield wiper system of claim 4, wherein: the ball nut includes a flange that defines a first passage; the windshield wiper system further includes: a first guide pin extending from the aft end wall of the housing to the aft end wall of the endcap such that the first guide pin is parallel to the aft shaft, wherein the first guide pin extends through the first passage in the flange of the ball nut and prevents rotation of the ball nut relative to the stator when the aft shaft segment rotates.
 6. The windshield wiper system of claim 5, wherein: a second passage is defined by the flange of the ball nut; and the windshield wiper system further includes: a second guide pin extending from the aft end wall of the housing to the aft end wall of the endcap such that the second guide pin is parallel to the aft shaft segment and is spaced apart from the first guide pin, wherein the second guide pin extends through the second passage in the flange of the ball nut.
 7. The windshield wiper system of claim 6, wherein the first guide pin and the second guide pin are connected to the aft end wall of the housing.
 8. The windshield wiper system of claim 1, wherein the reversible motor is a reversible brushless direct-current motor.
 9. The windshield wiper system of claim 1, wherein the reversible motor is configured to stop responsive to the ball nut contacting the aft stop while the aft shaft segment rotates.
 10. The windshield wiper system of claim 9, wherein the reversible motor is configured to stop responsive to sensing an increase in current drawn by the motor when the ball nut contacts the aft stop while the aft shaft segment rotates.
 11. The windshield wiper system of claim 1, wherein the reversible motor is configured to stop responsive to the ball nut contacting the forward stop while the aft shaft segment rotates.
 12. The windshield wiper system of claim 11, wherein the reversible motor is configured to stop responsive to sensing an increase in current drawn by the motor when the ball nut contacts the forward stop while the aft shaft segment rotates.
 13. The windshield wiper system of claim 1, wherein the aft shaft segment is threaded, and the system further includes balls within the ball nut that engage the threads on the aft shaft segment, whereby the ball nut translates forward and aft when the aft shaft segment rotates.
 14. The windshield wiper system of claim 1, further comprising: a reduction gear that rotationally couples the aft shaft segment to the wiper arm.
 15. The windshield wiper system of claim 14, wherein a pinion gear is defined by the forward shaft segment, and the pinion gear is rotationally coupled to the reduction gear.
 16. An aircraft including the windshield wiper system of claim
 1. 17. A method of operating a windshield wiper system, comprising: driving a rotor of a reversible motor relative to a stator of the reversible motor; driving an aft shaft segment of a motor shaft with the rotor; translating a ball nut from rotation of the aft shaft segment between a forward stop and an aft stop; and stopping the reversible motor when the ball nut contacts either of the forward stop and the aft stop while the aft shaft segment rotates.
 18. The method of claim 17, further comprising: driving a reduction gear with a forward shaft segment of the motor shaft and driving a wiper arm with the reduction gear.
 19. The method of claim 17, further comprising: preventing rotation of the ball nut relative to the stator with a guide pin extending through a passage defined in a flange of the ball nut, from the forward stop to the aft stop.
 20. The method of claim 17, further comprising: stopping the reversible motor responsive to sensing an increase in current draw by the motor when the ball nut contacts either of the forward stop and the aft stop while the aft shaft segment rotates. 